To avoid electromagnetic interference (EMI) generated by high frequency signals, frequency jittering is a method that is often used in high frequency electronic products. Conventionally, frequency jittering is achieved by means of a digital counter; following the counts generated by the digital counter, the frequency shifts within a narrow range. The digital counter may be designed to provide sequential or random counts, and the frequency correspondingly shifts sequentially or randomly. A typical frequency jittering control circuit employing a digital counter may be found in U.S. Pat. No. 6,229,366.
The drawbacks to use a digital counter are as follows: first, a digital counter is a huge circuit device; it is made of T flip-flops, and T flip-flops heavily consume circuit area. Moreover, in such frequency jittering control circuits, a designer has to design current source devices of different current amounts, and the corresponding control mechanism of the different current source devices by the output of the digital counter. Thus, the conventional circuit employing a digital counter is disadvantageous in that it is costly and complicated.